1. Fields of the Invention
The present invention relates generally to apparatuses and methods of preventing cracks and leaks in engine exhaust systems in vehicles, and, more particularly, to a bellows assembly for preventing cracks in the exhaust stack or shroud of an aircraft.
2. Discussion of Background and Prior Art
Shown in FIGS. 1, 2 is a small passenger aircraft 10 with dual turbo-prop engines 11, 12, such as the King Air 200 and B200 family of aircraft made by Raytheon. A typical turbo-prop engine 20 receives outside air in an air inlet 21 leading to a 3-stage axial flow compressor 22 which sends compressed air to a centrifugal compressor 23. The highly compressed air is then mixed with fuel and burned in the combustion chamber 24 the exhaust gases from which are accelerated through the nozzles of a compressor turbine 24 and then are finally expanded through the nozzles of a free power turbine 26 which drives a high speed shaft 27 which, after reduction of the shaft rpm in a gear box 28, drives the propeller shaft 29 and propeller, while the spent gases are exhausted through exhaust outlets 30 to the engine exhaust stacks 42, 54 (FIG. 3).
Most OEM aircraft in the King Air 200 class come with an air inlet anti ice system, and the King Air 200 is no exception. In a typical aircraft, the original inlet anti-ice system included a pair of pick up tubes 44 (FIGS. 7, 8), one each (right and left, relative to the nose of the aircraft looking forward) connected between an exhaust stack 42, 54 adjacent the engine nacelle 32 and an air frame heater duct 74, 82 in the lower engine cowling 71. Each pick up tube 44 (FIGS. 7-12) is bent about 80.degree. (FIG. 9), has an upper end 50, 66 welded around a hole in the stack wall and is fluidly coupled to a scupper portion 46, 58 mounted inside the stack 42, 54, the open end 48, 60 of which faces upstream relative to the exiting exhaust gases, thereby receiving and directing some exhaust gas forwardly through the elongated portion 45, 64 of each tube 44 through the lower end 52, 68 of the tube which is slip joint 84 fastened 87, 88, 89 via donut 85 and duct flange 86 (FIG. 5) to the airframe ducts 74, 82. Ducts 74, 82 are part of the inlet 77 anti-ice system of each engine and direct the hot exhaust gases through ducts 76 which terminate at splitter vanes 78 which dump the spent exhaust gases to the atmosphere through the opening 80 in exhaust outlet plate 79 in the airframe skin at the bottom of the lower cowling 71.
One problem with this design is that soot accumulated on the lower surface of the cowling and the underside of the wing. Accordingly, it is an object of the present invention to provide an inlet anti-icing system that eliminates the accumulation of exhaust gas soot inside the cowling and on the exterior skin of the aircraft.
Another problem with this original design was the possibility of exhaust stack cracking. Significant engine vibrations in the X, Y and Z directions, such as during start-up, shut-down, taxiing, take-off, landing, rapid throttle movements, turbulent air conditions, certain sustained engine operating conditions, and the like, and also as a result of repeated expansion and contraction resulting from the combination of extreme weather and operational temperature conditions, place a large amount of stress on the welded connection between the elongated pick up tubes 44 and the stack 42, 54 walls at the point of attachment. This stress has resulted in the cracking of the pick up tube to stack welded connection allowing further hot exhaust gases and soot to escape into the space between the exterior wall of the stack and the engine cowling creating a potential fire hazard and a dirty, unsightly appearance throughout the entire main engine compartments.
Accordingly it is a further object of the present invention to provide an inlet a anti-icing system that eliminates the cracking of exhaust stacks and associated couplings and the further accumulation of exhaust gas soot inside the entire engine cowling and main engine compartments.
A subsequent prior art system has only partially solved the above described problems. As shown in FIG. 13, this prior system modifies the inlet 77 anti-ice system to make it a flow through system in which exiting exhaust gases are picked up on the right side, as in the prior system, but are directed through the hot lip duct in one direction to the left side of the engine where they exit to atmosphere through the left exhaust stack, requiring modifications to the left side scupper, both pick up tubes and the lower cowling discharge area. The modifications made by this prior art system are shown in FIGS. 13-20, as explained in greater detail below.
In the modified prior art flow through inlet anti-ice system, the pick up tubes 44 are replaced by a pick up nipple 102 on the right side and exit nipple 124 on the left side. The right scupper 48 remains with its opening facing upstream creating a positive inlet pressure at that end of the system, while the left scupper 58 open face 60 is reversed to point downstream relative to the exhaust gases creating a suction at that end of the system. (FIGS. 16-20). The splitter vanes 78 in the hot lip are removed and blocker dams 126 are installed blocking the old exhaust outlets, leaving duct 76 as a single continuous sealed duct. Cover plate 128 replaces the prior plate 79 completely sealing the lower cowling area from the exhaust gases. Hose assemblies 104, 114 replace pick up tubes 44. Each hose assembly 104, 114 includes a curved tube having a slot 106, 120 in one end that fits over and is clamped 108, 122 to the stack nipple 102, 124 and a flange 112, 116 at the lower end that is fixedly bolted to a gasketed 113,115 airframe duct flange 74, 82.
To relieve stress in the rigid connections between the engine, stack, nipple, hose and heater duct, the central portion of each hose body is roughly bent at about 70.degree. and is formed with a plurality of outwardly extending convolutions 110, 118 which allow the body to flex like a bellows and dampen the engine vibrations previously described. However, in practice while the above solution has relieved the lower cowling problem, the main engine compartment problem previously described has not been solved because the flex in the bellows body itself has been proven to be insufficient to prevent the continued cracking at the nipple-stack welded joints due to the oftentimes severe engine movements in the X, Y, and Z directions. Accordingly, as previously stated, it is an object of the present invention to prevent the cracking of the stacks due to such engine movements.
In view of the failed prior attempts there is a long felt need for and it is an object of the present invention to provide a satisfactory hot inlet lip anti-ice system for small twin turboprop aircraft.